1. Field of the Invention
The present invention relates to the charging of furnaces and particularly to the delivery of material from the ambient atmosphere to the interior of a furnace and the exercise of control over the distribution of the thus delivered material on the furnace hearth. More specifically, the present invention is directed to charging installations for shaft furnaces and particularly to devices for transmitting material to the interior of a pressurized furnace and controlling the distribution of such material within the furnace. Accordingly, the present invention is directed to novel and improved methods and apparatus of such character.
2. Description of the Prior Art
Generally speaking, charging installations for blast furnaces fall into two classifications. The older type of charging installation is characterized by "bells" which perform a valving and flow control function. The other type of furnace charging installation is the "bell-less" type as exemplified by the apparatus disclosed in U.S. Pat. No. 3,693,812. Furnace charging installations of the "bell" type include a plurality of superimposed charging bells which are individually raised and lowered in accordance with a sequence which permits the material with which the furnace is to be charged to be conveyed from the ambient atmosphere to the interior of the furnace at the top or throat area thereof.
Prior furnace charging installations which employ charging bells are known to possess a number of inherent deficiencies when compared to the "bell-less" type of charging installation. These deficiencies include manufacturing problems and furnace operational difficulties. The seriousness of these problems increases in proportion to the dimensions of the charging apparatus and the furnace pressure. In a bell-type charging installation the lower bell, which is the largest in the series of superimposed bells, functions both as a distributor for the charge material released into the furnace and as a shut-off valve which delimits a chamber in which the charge material is temporarily stored. Because of its size and the multiple functions it must perform, the manufacture of a lower charging bell involves major production problems and these problems are aggravated when it becomes necessary to service the installation by removal and replacement of the bell. Also, during normal operation, a considerable amount of equipment is required for raising and lowering the bells, particularly the lower bell, and for establishing the requisite pressure in the chambers which are in part defined by the bells. The complete charging installation thus requires powerful actuators and is usually of considerable height.
One of the major deficiencies of the prior bell-type charging installations resides in the fact that there is practically no way to exercise control of the distribution of the charge material on the charging surface of the furnace. Since the larger lower bell of a bell-type charging installation is in the shape of a truncated cone, it is impossible to avoid the formation of a cavity or depression at the center of the furnace and usually also about the periphery of the charging surface. Thus, charging installations of the bell type are characterized by the establishment of a charge profile which, when viewed in cross section, has the known "M curve". It is well known in the art that the efficiency of operation of a blast furnace may be maximized by controlling a number of operating parameters including the charge profile. For a further discussion of the reasons why exercise of control over the furnace charge profile is important, reference may be had to U.S. Pat. No. 4,094,494. For purposes of the present discussion it should suffice to point out that it is highly desirable to be able to exercise control over the deposition of charge material on the furnace charging surface or hearth and that this operating parameter cannot be controlled in a conventional prior art bell-type charging installation.
There have been efforts to overcome or reduce the seriousness of the above-discussed inherent problems with bell-type furnace charging installations. These efforts have included the positioning of detectors about the lower bell of the charging installation, increasing the number of superimposed bells and modifying the equipment for operating the bells. These efforts have, to date, been largely unsuccessful and have often resulted in proposed solutions which were either economically impractical or would require an unacceptable increase in the overall height of the charging installation which, of course, is mounted on the top of the furnace. Accordingly, most newly constructed large capacity furnaces are equipped with "bell-less" charging installations which include a rotary and angularly adjustable charge distribution chute located within the furnace.
Economic and/or physical limitations may, however, preclude the replacement of a conventional bell-type charging installation with a "bell-less" type installation in some cases. Thus, by way of example, when an existing blast furnace is being repaired, the ability to retain the auxiliary equipment associated with a bell-type charging installation may dictate that the bell-type charging device not be replaced by a "bell-less" charging installation. There thus remains in the industry a strong desire, previously unanswered, for apparatus and techniques which permit a bell-type charging installation to be upgraded in such a manner that true exercise of control over furnace charge profile is possible.